Density responsive device



VMay 11, 1949.

E. A. HAAsE :my

DENSITY RESPONSIVE yDEVICE Filed Ilarch 6, 1944 wf/v 50. rais R14-Hansa.IIIIIIIIII lll l ATTMIVEY Patented May 17, 1949 DEN SITY RESPONSIVEDEvICE Elmer A. Haase and Jay A. Bolt, South Bend, Ind., assignors toBendix Aviation Corporation, South Bend, Ind., a corporation of DelawareApplication March 6, 1944, SerlalNo. 525,278

A 2 claims. (ci. zas-'92) A V type may, for example, be used in acarburetor to control theV area of the fuel metering orifice to therebycontrol the fuel/air ratio; or it may be used to modify the air meteringdifferential pressure used in regulating the fuel flow to thereby varythe fuel ilow and consequently the fuel/air ratio; or it may be used inother ways to control the ratio of fuel and air being supplied by thecarburetor to the engine.

An object is to provide a density-compensat-- ing unit of the singlebellows or capsule type having certain features of construction whichresult in improved performance characteristics.

Another and more specific object is Ato provide a density controlcapsule or bellows embodying a valve element which will be automaticallymoved to a safety position in the event of bellows failure.

Other objects and advantages will become apparent in view of thefollowing description taken in commotion with the drawings, wherein:

Figure 1 is a view. principally in substantially central verticalsection of an injection-type carburetor having the improved control unitof the present invention operatively applied thereto;

Figure 2 is a transverse vertical section of the control unit of Figure1;

Figure 3 is a top plan of Figure 2; and

Figure 4 is an enlargement of the lower por- -tion of Figure 2.

The construction of the improved control unit per se will iirst bedescribed, next the method of filling the same, and finally itsadaptation to, and operation in connection with the injection typecarburetor` of Figure 1.

Referring particularly to Figures 2, 3 and 4,

` 2 Il, abutting at its lower end against a shoulder I2-b forming partof member I2 and at its upper extremity against the'- top transversewall I5 of cap II. The spring Il prevents 4collapse of the bellows whenthe latter is evacuated, as will be more fully hereinafter explained.

A combined dash-pot piston and guide member I6 is inserted in an openingformed in the end wall I5 of cap II and has a ange Il secured inleak-proof relation thereto. IThe lower extremity I6a of the member I6has a sliding fit in the cylinder i3 and functions as a dash-pot pistonwith respect to said cylinder and also as a guide for the bellows, Themember I6 is formed with a ll port I8 which connects-with a cross-portIBa communicating with the interior of the bellows I0, the upperextremity of the port I8 being enlarged and internally threaded toremovably receive a sealing plug I8b. The-body of the piston I6a ispreferably formed with a relieved portion indicated at I9 to facilitatelubrication of the side walls thereof.

The top wall I5 of head or cap II may be provided with a plurality offins 20 which render the device more sensitive to changes in temperatureIn that they expedite transmission of heat to the wall I 5 and thence tothe interior of the cap, the latter preferably being fllled orpartlyfllled with a temperature-responsive medium other than air in amanner to be described. s

At its lower extremity, the cylinder I3 is formed with one or aplurality of restricted ports 2|, whereby oil or other damping fluid ispermitted to pass from said cylinder into the bellows and return whenthe bellows is compressed and extended and relative reciprocatorymovement ensues between the piston and cylinder, to thereby moreeffectively damp vibration of the bellows.

The parts this fardescribed constitute a bellows assembly which iscarried by a housing 22, the latter at its lower extremity beingthreaded into a supporting bushing 23 provided with a lock nut 24, said`bushing having a lower projection or boss 25 adapted to be threadedinto a socket provided therefor in a stationary support, such as thedeck or top wall of a carburetor, note Figure 1.

A valve member or needle 26 is carried by the movable end of thebellows, said needle at its upper end being' secured to an annular disc21 which rests on a retaining Washer 28 removably held in place by aresilient snap ring 29 adapted to engage in a groove formed in the innerwall of the member I2. A plunger 30 is inserted in a bore formed in theupper extremity of the needle 26 and is normally urged against thebottom wall of the member I2 by a spring 30a, to thereby resilientlymaintain the said valve in its assembled position and permitself-alignment.

The needle valve 26 is preferably of the slab type and is slidablewithin a sleeve 3| having a press t in a bore formed inl the centralportion of bushing 23, the lower end of the said needle preferably beingtapered or beveled and cooperating with a transverse port or passage 32.An overtravel by-pass port or slot 33 is formed in one side of theneedle and functions as a safety means in the event the bellows shouldbreak, as will be more fully hereinafter described.

A lock nut 34 is threaded over the cap lIl and contacts the upper end ofhousing 22, to ensure against displacement of the bellows and coactingparts.

A seat member 35 is provided at the lower end of the boss and has anexternal annular groove adapted to receive a sealing gasket when theunit Yis mounted as shown in Figure 1.

The unit herein illustrated is of the venturivented type, andaccordingly the bushing 23 is formed with air-inlet vents or ports 36which communicate the bellows with the main venturi of the carburetor,calibrated ports 36a in the upper extremity of the bellows housingcommunicating the bellows with the air scoop. This places the bellows inpressure communication with the air flowing through the venturi as wellas the air in c the region of the carburetor deck whereby the loaded,and its spring rate per given size or unit capacity are factors whichhave an important bearing on the temperature and density compensatingcharacteristics and accurate metering of the unit. Theoretically, abellows with no spring force or effect exerted at any time would Aresultin substantially similar internal and external pressures and travel ofthe needle valve or element controlled thereby in direct relation todensity for any temperature, but from a practical standpoint, thiscannot be achieved. In the present invention, a bellows is used having arelatively low spring rate` per unit capacity or for a given stroke ofthe bellows, and the errorv remaining due to spring eifect is offset bypredeterminedA evacuation. By stroke is meant the axial travel ormovement of the bellows to carry the needle valve over the range ofmovement it -must have to properly control the valve port. Spring rateof the bellows is influenced primarily by the number of activecorrugation per given stroke, wall thickness of the bellows, and type ofmaterial from which the bellows is made. The stroke that a given sizebellows will have under load is directly proportional to nthe number ofactive corrugations and inversely proportional to some power of wallthickness. In the example illustrated in Figure 2 of the drawings, thebellows has eleven active corrugations with side walls of berylliumcopper of single ply thickness. However, when spring rate is reducedbeyond a certain point, a problem presents itself in that the bellowstends to become unstable in operation, particularly during the time itpasses from a state of expansion and begins to contract, as where itmoves from a high to a lower altitude. To more accurately control thetravel of the bellows, a larger quantity of oil-or other damping fluidis used than is the case with bellows having less flexibility. This hasa stabilizing imiuence and has given satisfactory results.

Another important factor to be considered is the degree of evacuation ofthe bellows. According to the present invention, the bellows isevacuated at ground level barometer to an internal pressure equivalentto some external pressure which prevails at a relatively high altitude,for example, to a pressure approximating those prevailing at an altitudeof 20,000 feet and which would be in the neighborhood of 14" Hg absolutepressure. Thus, when abellows evacuated in this manner is used for acontrol on an aircraft carburetor, up until the time external pressuresdrop to a certain point, the internal gas pressure of the bellows isless than the external pressure thereon. When so evacuated and withcoordinated spring loading, the major part of the effective stroke ofthe bellows will take place while the bellows is in compression and theminor part while the bellows is in tension. This may be controlled bygreater or less evacuation with' coordinated spring loading, dependingupon the installation or the type of airplane to which the unit isadapted. As long as the bellows operates in a state of compression, theerror introduced by spring effect is negligible. It should beunderstood,v however, that a spring-loaded bellows evacuated at groundlevel to a pressure corresponding to that existing at some particularaltitude will not necessarily have an internal pressure equal to suchaltitude pressure when that particular altitude is attained, since theinternal volume of the bellows is constantly changing with changes inaltitude. Hence, the internal pressure might be materially less thanexternal pressure at 20,000 feet altitude, and the point where internaland external gas pressure become equal be considerably beyond suchaltitude.

Evacuation coordinated with spring rate and oil flll must be maintainedwithin certain limits, else the unit will have insufllcient temperatureresponse and there will be increased error in this direction.Furthermore, evacuation beyond a certain point requires an unduly heavyspring to maintain the bellows in the desired state of compression atground level barometer which introduces an error in density compensationin the region of low altitudes. Experiments have indicated a lower limitof pressure within the bellows at ground level of within theneighborhood of 10 Hg absolute pressure.

Instead of considering the degree of evacuation in terms of internalabsolute pressures, it maybe given as the amount of internal depression.Thus with a barometric pressure of 29.5" Hg, an internal depression of12.0 Hg would correspond to 17.5" Hg absolute internal pressure, aninternal depression of 15.75 Hg to 13.75" Hg absolute internal pressure,an internal depression of 22.5 to 7" Hg absolute internal pressure, etc.

As far as the upper limit is concerned, here the line need not be sosharply drawn. Obviously, the less evacuation, the less will be therange of bellows travel in compression and the more the range of travelin tension.

When a bellows is evacuated as above set forth,

u it becomes necessary to prevent undue collapse thereof, or to`maintain it in a predetermined state of compression. This isaccomplished by the spring I4, which should be of such strength as tomaintain the bellows in the desired condition '5 with a certain quantityof dampingiiuid, pref- 1o eiably a good grade of petroleum oil. lAcertain ratio of dampingfluid and temperature-responsive gasmust beobserved. AThe amount of fluid determines the enclosed gas volume, andsince oil (if used) is affected by temperature, it will 15 tend to giveadditional temperature compensation in the compression travel of thebellows and less temperature compensation in the extension travel of thebellows.

Figure 1 illustrates an adaptation of the im-H20 proved control unit toan injection type carburetor, only such parts of the latter being shownas will permit an understanding of the operation of the unit. Briefly,the carburetor comprises a casing or housing, generally indicated at 31,having a main venturi 38 and a small or boost venturi 39. Air pressuredifferential chambers are indicated at 49, 4i and fuel pressuredifferential chambers at 42 and 43. Chambers 49 and 4| are separated bya flexible diaphragm 44, while chambers 42 and 43 are separated by likediaphragm 45. A rigid wall 46 separates chambers A4l and 42 and alsoserves to support a fuel-inlet valve assembly mounted for reciprocatorymovement in the center of the respective chambers and adapted to move inrelation to the movement of the diaphragms 42 and 43 to open afuel-inlet port, not shown, for admitting unmetered fuel into thechamber 43, from which it flows to a regulator section, also not shown,through various meter- 40 ing orifices, not shown, to a discharge nozzle49. The chamber 42 is subjected to metered fuel pressure, or in otherwords to the pressure of the fuel posterior to the metering orifices.The fuel metering differential pressure is thus applied 45 across thediaphragm 45.

The chamber 40 is connected to the air scoop by means of impact tubes 5i, annular chamber.52,

passage controlled by needle valve 26, and thence by way of passage 53;and chamber 4I is 50 connected to boost Venturi 39 by means of passage54. When the engine is in operation,- air is drawn in through the airscoop and thence through the venturis 38 and 39 and a differentialpressure is created between the throat of venturi 55 39 and the airinlet which, at constant entering air density, is proportional" to thesquare root of the quantity7` of air flowing. These respective pressuresare transmitted to chambers 49 and 4l and create a net force ondiaphragm 44 tending 60 to move valve `assembly 41 to the right, or in adirection to open the valve. If this force were unopposed, the valvewould move to the extreme right; however, when the valve opens, fuelunder pressure flows into unmetered fuel `chamber 43,

through the metering orifices, and thence to the discharge nozzle 49from which it is discharged into the air stream flowing to the engine.The fuel metering differential pressure across the metering orificeresulting from or accompanying the flow therethrough, is transmitted tochambers 43 and 42, and acts upon diaphragm 45 creat` ving a forcetending to move the fuel inlet valve to the left, or in a direction toclose the valve,

thus opposing the force created on diaphragm 16 6 44 by the airdierentlal pressure. The valve will therefore adjust itself to a pointof equilibtrolledy by the rate of air flow, and a constant mixture offuel and air obtained.

For a more comprehensive disclosure of the in- Y jection carburetordisclosed in Figure l, referencermay be had to the copending applicationof Frank C. Mock, Serial N o.'202,206, filed April 15, 1938, Patent No.2,390,658.

Since the venturi to air scoop differential pressure increases for agiven mass rate of air flow upon decrease in entering air density, thedifferential pressure across diaphragm 44 will tend to increase therebyincreasing the fuel flow 4and richening the mixture. In order to preventsuch enrichment with increase in altitude, the carburetor of Figure 1 isprovided with a. calibrated bleed 56 interconnecting chambers 40 and 4iwhich is substantially ineffective to vary the pressures in chambers 40and 4I at such times as the needle 26 is an open position, as at groundlevel, but which becomes increasingly effective in reducing the pressurein chamber 40 as the density responsive needle 26 progressivelyrestricts passage 55 with increase in altitude. Asa consequence, for anygiven mass air ow the needle 26 will so restrict passage 55 withvariation in altitude that the differential in pressures acrossdiaphragm 44 remains constant notwithstanding that the differential inthe pressures at venturi 39 `and impact tubes 5| increases with decreasein entering air density. By this means, automatic altitude compensationis obtained and the richness of the mixture is unaffected by variationsin altitude, as is desired.

For example, as the density of the entering air decreases, as by anincrease in altitude or rise in temperature, the air differentialcreated by the main and boost venturis increases for a given weight ofair and tends toward enrichment of the fuel mixture. However, suchdecrease in density acts onbellows I0, which expands and causes theneedle valve to lower and restrict passage 55, thereby reducing thedifferential across the diaphragm 44 and the fuel valve tends to closeand regulate fuel flow in proper ratio to mass air flow. Upon anincrease in density, as where the plane descends from a high to a lowaltitude, the reverse takes place. The fuel mixture is thus maintainedat all altitudes at the i proper richness or value.

Bellows failure is very rare, but should such occur, the needle valve 26will immediately be projected to the position shown in Figure 4, whereinstead of closing off passage 55 from passage 53,

and thereby greatly leaning the mixture, the slot emergency settingwhich will give the pilot time to ground the plane without enginefailure due to severe leaning out of the mixture.

It will be noted that the heat transfer ns 20 are located at a pointwhere maximum heat transfer is desirable, viz., in the region of the capcontaining the temperature-responsive fluid or nitrogen.

Although the invention has been described with reference' to aparticular embodiment, it will be understood that certain changes inconstruction and design as well as in the steps of the method could beadopted without departing from the scope of the invention `as defined bythe appended claims.

We claim:

1. A density-responsive control unit for actuating a regulating elementsuch as a needle valve in accordance with changes in pressure andtemperature over a certain altitude range including a corrugated bellowshaving a; movable end, means connected to said latter end mounting saidelement, a cap at the opposite end of the bellows, supporting means towhich said cap is secured, a hollow cylinder located centrally of thebellows and fixed to said movable end, a piston member projecting fromsaid cap into said cylinder, said bellows being partly evacuated to aninternal pressure corresponding to a pressure existing at an altitudewell above normal ground level, a spring in said bellows encircling saidcylinder and piston and functioning to sustain the bellows againstabnormal collapse at ground level barometer due to evacuation, a dampingfluid partly iilling the bellows and a temperature-responsive inert gasfilling the space above the damping fluid, said cylinder beingported tothe interior of the bellows to provide a dash-pot action duringextension and contraction of the bellows.

2. A density responsive device for controlling .a valve arrangedtoregulate the flow of a fluid through a port, including a corrugatedbellows having a movable end and a relatively xed end,

meanssupporting said valve member from said movable end, said bellowsbeing evacuated to an internal depression such that the internal gaspressure thereof is less than external pressures over a substantialportion of the altitude range,

spring means of such force as to balance the REFERENCES CITED Thefollowing references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 897,730 Fulton Sept. 1, 19081,251,214 Fulton Dec. 25, 1917 1,477,277 Milker Dec. 11, 1923 1,752,116Smith Mar. 25, 1930 1,802,848 Summers Apr. 28, 1931 1,934,548 KelloggNov. 7, 1933 2,088,954 Gregg Aug. 3, 1937 2,112,750 Price Mar. 29, 19382,116,802 Shivers May 10, 1938 2,129,499 Landon Sept. 6, 1938 2,155,950Nallinger Apr. 25, 1939 2,214,236 Seldon Sept. 10, 1940 2,250,932Kittler July 29, 1941 2 297,231 Lichte Sept. 29, 1942 2,307,724 AndersonJan. 5," 1943 2,316,417 Gregg Apr. 13, 1943 2,352,058 Wood et al June20, 1944 2,361,227 Mock Oct. 24, 1944 2,376,711 Mock May 22, 1945 OTHERREFERENCES Automotive Industries, June 15, 1941, pages 620-624.

